No two diamonds are the same. A diamond's most distinguishing characteristics are its inclusions or marks that are often invisible to the naked eye. However, under a jeweller's magnifying loupe or microscope they can look like crystals, tiny rivers, or clouds. A diamond's clarity is determined by the presence or absence of inclusions--fewer inclusions mean better clarity--and how visible they are. The greater a diamond's clarity, the greater its brilliance and value. A diamond categorised as internally flawless will have no inclusions, but this is extremely rare. Diamonds with very, very small inclusions are graded as VVS1 or VVS2. Those with larger inclusions appear lower down the grading skill. Diamonds with inclusions that are visible with the naked eye are graded I1 to I3.
A flawless gemstone is rare and usually extravagantly priced. As with diamonds, most gemstones have inclusions, or tiny mineral flaws, that can be seen under magnification or by the careful eye. Sapphires tend to be moderately included, while emeralds and rubies are usually heavily to moderately included. Clarity grades range from VVS (very, very slightly included) to I3, in which inclusions are quite prominent and can affect the gemstone's beauty.